Hybrid polyMOF Materials Prepared by Combining an Organic Polymer with a MOF and Their Application for Solar Thermal Energy Storage

The combination of metal–organic frameworks (MOFs), namely UiO-66, with polyethylene glycol (PEG) polymers yields hybrid polyMOF materials, which show unique morphology with tunable characteristics of UiO-66. Mixed MOF-PolyMOFs (referred to as UiO-66) are utilized as a support material for the preparation of shape stabilized phase change materials (ss-PCM). Three ss-PCMs were synthesized with the composition of PEG-0.5 g/UiO-66–0.2 g (PU-0.5), PEG-0.7 g/UiO-66–0.2 g (PU-0.7), and PEG-1.0 g/UiO-66–0.2 g (PU-1.0) and tested for solar thermal energy storage. The high PEG retaining capacity of UiO-66 is promising for thermal storage applications. The latent heat value of the PU-0.5 PCM is 146 J/g, which is considerably higher than that of PCMs based on similar materials. Besides, PU-0.5PCM has a high energy storage efficiency, high thermal energy capability, and exceptional shape-stabilized PCM properties. Thermal conductivity of PU-0.5 PCM is 0.51 W/mK, which is higher than that of most of the reported paraffin- and PEG-based PCMs. PU-0.5 PCM remains stable even when subjected to 200 freezing and melting cycles. In addition, the use of carbon nanotubes (CNTs) to improve the thermal conductivity of PEG-UiO-66 has been investigated. For comparison, the effect of PEG of various MWs (molecular weights) was also calculated.